T lymphocytes mature in the thymus where they apparently learn to treat the thymus H-2 antigens as self markers i.e. F1(H-2b/H-2d) T cells matured in a H-2b thymus are all H-2b restricted. We will investigate whether T cell differentiation occurs more efficiently when stem cells and the thymus are H-2 matched than when the cells are completely H-2 mis-matched. Mice bearing thymus grafts of different H-2 type will be lethally irradiated and injected with stem cells of one H-2 type. We will then determine whether there is preferential homing or maturation in the syngeneic thymus. What type of cell can directly present antigen to virgin cytotoxic T cells will also be studied. Whether "pure" T cells, B cells or only some other type of specialized presenting cell can do this is controversial. The specificity of certain monoclonal antibodies secreted by cloned hybridoma cell lines will be investigated. We will study the antigens tissue distribution, molecular characteristics, and whether they fit with any known surface antigens.